Stargazers around the world are setting up special telescopes and passing out cardboard eclipse glasses to view the once-in-a-lifetime sight of Venus passing in front of the sun.

The transit of Venus – a planetary spectacle that won't occur again until 2117 – won't be enough to significantly block the sun's light but it will give Earth's closest star a moving beauty mark.

The transit is happening during a six-hour 40-minute span starting just after 6pm EDT in the US (11pm BST). What can be seen and for how long depends on the sun's activity in particular regions during that exact window, and the weather. Those in most areas of North and Central America will not see the start of the transit until the sun sets, while those in western Asia, the eastern half of Africa and most of Europe will catch the transit's end once the sun comes up.

Hawaii, Alaska, eastern Australia and eastern Asia including Japan, North and South Korea and eastern China will be able to see the entire event because the transit will happen during daylight in those regions.

Observers are advised not to stare directly at the sun without eclipse glasses, a properly filtered telescope or a strong welding visor – permanent eye damage could result.

Astronomers across the globe are using the rarity of the event to spark public curiosity and to document the transit.

In Hawaii, university astronomers have planned viewings at Waikiki Beach, Pearl Harbor and Ko Olina. At Waikiki, officials hope to show webcasts of the transit as seen from telescopes from volcanoes Mauna Kea on the main island and Haleakala on Maui.

Nasa plans a watch party at its Goddard visitor centre in Maryland with solar telescopes, images from its solar dynamics observatory mission and featuring expert commentary and presentations. The observatory will produce "Hubble-quality" images, according to Nasa's website.

Groups of scientists from the University of North Texas will watch from points in Alaska and Hawaii to recreate the 1769 expedition of James Cook, who used the transit to calculate Earth's distance from the sun. The scientists will use atomic clocks, GPS and high-end telescopes to take measurements, and as well as capturing timelapse video.

This will be the seventh visible transit of Venus since German astronomer Johannes Kepler first predicted the phenomenon in the 17th century. Because of the shape and speed of Venus's orbit around the sun and its relationship to Earth's annual trip, transits occur in pairs separated by more than a century.

The transit is not as dramatic as a total solar eclipse, which sweeps a shadow across the Earth, but there will be six more of these across different parts of the globe during this decade alone.